This invention relates to mass transfer devices for an exchange column and, more particularly, to structured packing elements used for facilitating mass transfer between fluid streams flowing within the column.
In various types of exchange columns, gas and liquid streams or two liquid streams are contacted with one another to effect mass transfer between the fluids. In many instances, structured packing elements formed of corrugated plates are used to facilitate contact between the fluids for enhanced mass transfer. These plates are typically positioned parallel to the column axis and are arranged so that the corrugations of each plate are disposed at an angle to the column axis. The corrugations of each plate also extend at an angle to and are in contact with the corrugations of adjacent plates to create inclined flow channels for the fluid streams. Typically, the vertically extending plates fill the horizontal cross section of the column and multiple layers of these plates may be used to fill the desired vertical dimension within the column. If multiple layer of plates are used, the plates in adjacent layers are rotated with respect to one another to enhance the radial or lateral distribution and mixing of the fluid streams.
To facilitate fabrication and installation of the corrugated plates described above in exchange columns, particularly those columns having a large diameter, bundles or "bricks" of plates are assembled together and are positioned in side by side relationship to fill the horizontal cross section of the column. The plates in each brick are held together in various fashions such as by mesh banding around the plates, welding, or pins inserted through the plates. The bricks are generally six-sided and have differing shapes dictated by the size of the brick in relation to the cross-sectional dimension of the column, the shape of the column and the intended placement position within the column. Those bricks positioned centrally within the cross section of the column will normally have a cubic or rectangular shape while those bricks adjacent the column wall will be shaped to conform to the shape of the column wall. For example, in cylindrical columns, the outer perimeter bricks will have at least one curved end or side to conform to the curved shape of the column. The curved end of the brick is formed by using plates with progressively shorter widths. In some bricks, one end of the plates lies in a common vertical plane while the opposite end of the plates forms a curve to approximate the shape of the column wall. In other bricks, both ends form curved surfaces.
While the use of the packing brick construction has greatly eased the fabrication and installation of corrugated plates in exchange columns, the separation efficiency of these plates may suffer because of less than desired communication of liquid streams between the ends of adjacent bricks. Efficiency may further suffer as a result of vapor streams bypassing the desired flow paths and passing upwardly along the vertical gaps which may form between the vertical ends of adjacent bricks. A need has thus developed for a structured packing brick having increased separation efficiency.